Investigating Dynamic Weakening in Laboratory Faults Using Multi-Scale Flash Heating Coupled With mm-Scale Contact Evolution
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AbstractFlashweakening models typically show good agreement with the total magnitude of weakening in highspeed rock friction experiments, however deviations during the acceleration and deceleration phases, and at low and intermediate sliding velocities, remain unresolved. Here, we incorporate inhomogeneous mmscale normal stress evolution into a model for flash heating and weakening to resolve outstanding transient and hysteretic friction observed in laboratory experiments and to identify unique solutions to constitutive parameters. We conduced 37 rock friction experiments on Westerly granite using a highspeed biaxial apparatus outfitted with a highspeed infrared camera. We initiated velocity steps from quasistatic rates of 1mm/s to sliding velocities ranging from 300 to 900mm/s and conducted both constant and decreasingvelocity tests following the velocity step. Two sliding surfaces geometries were used to control mmscale lifetimes and resttimes. Constantstrength sliding is achieved within 23mm of initiating the velocity step in all constantvelocity experiments. Macroscopic surface temperature is inhomogeneous and increases with slip distance, velocity, and decreasing resttime. Weakening increases with sliding velocity and decreasing resttime. We combine thermal models with measured surface temperatures to constrain the evolution of local normal stress at the mmscale and incorporate this evolution into a flashweakening model that considers weakening at both the m and mmscale. The flashweakening model improves when the effects of mmscale wear processes are incorporated and multiscale weakening is considered, however some transient friction remains undescribed. Models will be advanced by further incorporating wear processes and by considering processes at the mmscale and above.
